The invention relates to surveillance or alarm systems and more especially to such a system comprising a pneumatic circuit serving to monitor the temperature of a component or of a room and to provide at least one output signal when the component or the room reaches a certain temperature.
SUMMARY OF THE INVENTION
One object of the present invention is to device such a system which has a simple and compact structure.
A further object of the invention is to provide such a system which utilizes sturdy components so that the system as a whole has a greatly enhanced reliability.
In order to achieve these or other aims appearing in the course of the present specification, the system of the invention comprises a hollow detector member placed in the vicinity of the component or room, whose temperature is to be monitored, containing a fluid under a gauge pressure. The hollow member is adapted to open when a critical temperature of the component or of the room is reached so that the hollow within the detector member is connected with the surroundings, and a sensor is connected with the said hollow of the detector member so as to respond to opening of the detector member and the ensuing fall in fluid pressure therein and to produce a signal capable of being processed.
One advantage of the invention is that it provides a reliably operating device making it possible for a temperature to be exactly ascertained or detected. Useful fields of application of the device are more especially in connection with fire prevention; the device simply react to an increase in temperature as caused for example by a fire and when a certain temperature threshold is exceeded may trip an alarm or an automatic extinguishing installation. The detector member may for instance be in the form of a solid hollow member which at one point has an orifice covered by a diaphragm which is destroyed when a given temperature is reached. It would furthermore be conceivable to have valve arrangements for closing the orifice, as for example valves operated by bimetallic elements so that the system of the invention may be used repeatedly without having to replace damaged parts. Owing to its simple design, the device of the invention is furthermore economical in price and there is the advantage that the system may be integrated in already existing surveillance and alarm systems. Another advantage is that the novel system may be easily modified and adaptation for different sizes of room or component may be simply undertaken by making suitable changes in the form of the detector member.
In accordance with one feature of the invention the detector member is made of plastic material in the form of a loop of stiff of flexible pipe which ruptures when it reaches a critical temperature. This form of the invention makes possible the utilization of a low-price detector member which in addition operates reliably. The laying of the detector member becomes an extremely simple matter, as for example in the form of a loop ranging all over the danger zone.
As a further preferred feature of the invention the detector member is provided with a test valve for checking its internal pressure and is connected with a pressure supply for maintaining the internal operating pressure within the member, while the sensor is placed between the pressure supply and the detector member.
Such a design of the invention will ensure that the internal operational pressure within the detector member is permanently kept at a constant level while it is furthermore possible to check the system during operation to see if the detector member is in fact still under its working pressure or if a non-detected leak has occurred at some point along it.
It is possible to have choke between the pressure supply and the sensor. This further development of the invention serves to ensure that there is in fact a sudden decrease in the internal pressure of the detector member when it opens. The choke prevents a swift flow of the fluid to make good the loss from the detector member so that reliable response of the sensor is ensured. This feature at the same time serves to make sure that the detector member is continuously in connection with the pressure supply via the choke so that any leaks in the detector member may be compensated for.
It is possible to have at least one check valve placed between the pressure supply and the sensor and allowing flow of fluid towards the detector member. This feature ensures that after failure of the pressure supply the device of the invention will still be operational because the internal pressure is maintained.
In order to check whether the system has responded at any time it is possible to have an indicator light. It is furthermore possible to have a readout for the actual internal pressure in the detector member so that leaks may be promptly noticed.
As a further preferred feature of the invention, between the pressure supply and the detector member it is possible to have a shut-off valve which closes the connection between the detector member and the pressure supply when the pressure goes to a value below the minumum pressure valve of the pressure supply, such valve operation being more especially brought about by operation of a pressure responsive switch upstream from the valve. Such a feature of the invention ensures that when there is a failure of the pressure supply, escape of fluid under pressure in the detector member is prevented. At the same time the pressure responsive switch may give an alarm signal.
The sensor and, if present, the check valve and the choke may be placed in a detector device. Two such detector devices may be placed on or in a block- or slab-like carrier of anodized aluminum so as to form a module-like surveillance unit therewith, which on the one hand is connected with the pressure supply and on the other hand may have detector members connected to it in a number the same as the number of detector devices.
In keeping with a further feature of the invention, the pressure supply and the detector member are adapted to be connected with the back panel of the carrier, which is in the form of a connection array, and then communicate with a supply duct and with pressure fluid ducts inside the carrier.
The topside of the carrier may be adapted to function as a component mounting facility having two component mounting areas for the detachable mounting of two sensors connected via a sensor duct in the interior of the carrier running from the sensor to a respective duct for fluid under pressure.
The fluid pressure ducts may be arranged to extend through the carrier, in the length direction thereof, to open at the front side of the carrier in respective female holes for a pressure checking gage.
The supply duct may extend in the length direction of the carrier between the two fluid ducts to open at a valve mounting area on the said component mounting facility, it being possible for a high speed charging valve to be detachably mounted on such valve area so that the said valve may communicate via a filling duct within the carrier with the two pressure ducts.
It is possible to have at least one check valve arranged in the charging duct which permits flow of fluid to the pressure ducts, and prevents it in the opposite direction, there being a separate check valve for each pressure duct.
The system may furthermore be so designed that the supply duct is connected directly with the pressure ducts via two branch supply ducts, provided with a check valve and/or a choke, and arranged at an angle to the length direction of the carrier and parallel to a top face thereof so as to be coaxial.
Furthermore branch supply ducts and branch ducts from the charging duct may open on the longitudinal sides of the carrier and be sealed by detachable sealing means, such ducts having larger diameters on the longitudinal sides so as to receive the check valves and chokes therein, which may be removed, as for example by unscrewing them.
The sensors may be L-like pressure sensitive switches, with one limb of the L-form carrying an electrical terminal from which the signals, produced when the pressure sensitive switch is actuated, may be taken. The other limb of the L-shape has a valve means and when the two switches are mounted the respective short limb of the one switch is adjacent the longer limb of the other switch.
In accordance with a further development of the invention, there is a panel of the front side of the carrier which has a push button switch for actuation of the high speed charging valve, an indicator light operated by a signal from the sensor and two pressure monitoring gages indicating the pressure in the pressure fluid ducts.
The system may furthermore be so designed that on the component mounting facility at the back side of the carrier there is an electrical circuit card connector which on the one hand is in communication with the sensors and the indicator light and on the other hand may be connected with an electrical controller responding to the signals from the pressure sensitive switches.
On the connection part of the carrier it is possible to have a central connection plug with continuous ducts provided with normally closed shut-off valves. This plug may be detached and its ducts communicate on the one hand with the pressure or supply ducts in the carrier and on the other hand may be connected with the ducts running to the pressure supply and to the detector members.
These further developments of the invention are characterized by a high degree of compactness so that large systems connected with a large number of detector members may be so built up that the state of the system may seen at a glance. A further useful effect of compactness is that connecting ducts or channels are short in length so that the device of the invention is very reliable and its components are placed close together. Even on a pressure supply failure lasting several days the system of the invention still remains operational. Its individual components employed are very robust, i.e. not easily damaged, so that the reliability of the system is increased. At the same time the individual components may readily be replaced, as for example if one should fail, and the system is readily serviced. It is more especially the above-mentioned development with a central plug which ensures that in the event of any replacement of one of the modular surveillance units being necessary, there will be no discharge of fluid from the supply ducts with a consequent loss of power. If a surveillance unit is removed the pressure supply and the supply ducts to the detector members are automatically sealed off. If then another surveillance unit is connected the system may become operational at once without delay, since one does not have to go to the trouble of charging the supply ducts with fluid, which would take some time. The device of the invention is further characterized by optimum availability of the system. In particular the feature involving the design of the carrier in the form of an aluminum block or slab makes it possible to avoid false alarms being given and owing to the redundant or duplicated arrangement of two detector members a main alarm is only raised when both of the detector devices indicate that there is a fall in pressure in the detector member.
Further details and features of the invention will be gathered from the following account of various embodiments thereof as shown in the drawings.